Detectors involving surface ionization posses high sensitivity and selectivity in detecting organic compounds containing a nitrogen heteriatom. For example, the threshold in detecting tertiary amines and their derivatives reaches 10.sup.-14 -10.sup.-15 g/s. The molecules of the air and saturated hydrocarbons are not practically detected. A surface ionization detector was, thus, used to create a sensitive gas analyzer for analyzing amines and their derivatives. As a rule, a relevant analysis procedure is aimed at detecting amines in gas mixtures in the air inside work spaces presenting electric and explosion hazards as regards operating conditions and composition of analyzed mixtures.
This feature imposes limitations on gas-analyzing means designed for operation under the above conditions, more specifically, on maximum voltages required for their operations.
Furthermore, gas analyzers characterized by a high analysis rate are needed to effectively check the amine content in work spaces. The known surface ionization detectors are characterized by a limited feed rate, a disadvantage associated with the fact the temperature of a thermoemitter is to a large measure dependent on the flow of the analyzed mixture.
There is known a diode device for analyzing organic compounds directly in the air (cf. E. Ya. Zandberg, N. I. Ionov, V. I. Paleev, U. K. Rasulev: "Indicator aminov v atmosphere na osnove galoidnogo techneiskatelya", Zhurnal Tekhnichoskoy Physiki, 1984, Volume 54, pp 1855, 1856). This device essentially represents a haloid leak detector and contains in a case a cylindrical thermoemitter made of molybdenum and heated on the inside with a platinum heater, and also an ion collector encompassing with a gap the cylindrical thermoemitter.
The mixture to be analyzed is directed into the gap between the cylindrical thermoemitter and the ion collector and a part of ionized molecules getting on the surface of the thermoemitter forms positive ions which are acted upon by an electric field and, in effect, reach the ion collector wherein they are recorded.
However, the foregoing device has been generally unsatisfactory due to the need for using voltages as great as 200 V for collecting ions formed on the surface of the thermoemitter. Such operating voltages prevent utilization of the disclosed device in premises characterized by electric and explosion hazards.
The closest prior art device is a surface ionization detector for analyzing amine gas mixtures (cf. E. Ya. Zandberg, A. G. Kamenev, V. I. Paleev, U. K. Rasulev: "Visokochuvstvitelny detector aminov i ikh proizvodnikh", Zhurnal Analyticheskoy khimii, 1980, Volume 35, No. 6, pp 1188-1194), which comprises a case with a cylindrical collector, housing a directly heated thermoemitter of coiled molybdenum wire whose axis is disposed in the direction of movement of the analyzed mixture in the case of the surface ionization detector. Molecules of the analyzed mixture getting into the thermoemitter are ionized and gathered at the ion collector under the action of potential applied to the thermoemitter, which is positive relative to the ion collector. The ions are detected int eh direction perpendicular to the direction of movement of the analyzed mixture in the case of the surface ionization detector. Therefore, potential as great as 200 to 300 V should be applied between the thermoemitter and the ion collector to provide for a condition when, after desorption from the thermoemitter, the ions are effectively gathered at the collector.
Moreover, the use of the thermoemitter representing a spiral leads to eddy flows of the analyzed mixture, which also necessitates the application of high potential.
However, the utilization of voltages as great as 200 to 300 V for effective collection of ions formed on the surface of the thermoemitter prevents the use of the disclosed device in premises characterized by electric and explosion hazards.